A feeding unit of a tray sealing machine is known from the EP 1574431 A1. The feeding unit comprises a double-track feeding conveyor and a double-track accumulating conveyor to feed trays, which arrive arbitrarily on the feeding conveyor, in connection with the accumulating conveyor as a group of trays with predetermined spacing to one another in a gripper system of the tray sealing machine to create an airtight packaging At a high performance and if the friction force and/or grip of the trays in the accumulating conveyor is impaired for example due to contamination by liquid product remainders, the system will reach its limits In this context, major position deviations of the trays in relation to one another and of the group may occur.